Trees and Sidewalks: Creative Solutions

Rights-of-way have limited space, but we try to fit a lot into them: streets, sidewalks, overhead and underground utilities, as well as trees and other vegetation. Conflicts can arise between uses, notably trees and sidewalks. SDOT Urban Forestry works closely with Street Maintenance, Capital Projects, and private property owners to facilitate fixing sidewalks while preserving trees wherever possible. Innovative solutions for tree preservation include expanded tree pits and planting strips, rerouting sidewalks, ramping or bridging over tree roots, temporary shims and root pruning.

While expanding planting areas and ramping over roots, we must conform to sidewalk widths and slopes required by the Americans with Disabilities Act. Root pruning consists of cutting shallow roots in order to make room for a new sidewalk. Roots must be cut cleanly, ideally where other roots branch off to redirect growth. Pruning roots is challenging, as it’s necessary to remove enough roots to install a new sidewalk that will last, while leaving roots to sustain and support the tree.

There are certainly times when trees can’t be saved. When the available planting area is too narrow, the safety of a tree would be compromised by root pruning, or a tree is in poor condition regardless of sidewalk repair, removal and replacement is the only option. Despite all the challenges of accommodating trees and sidewalks, Arboriculturist Lou Stubecki, Urban Forestry’s lead on tree-sidewalk issues has an impressive record of saving trees. In 2010, of the 259 trees that had sidewalk repaired next to them, 191 were saved with a total appraised value of $1,645,530 and 68 trees had to be removed with a total appraised value of $252,630. When replacing trees or planting new areas, we choose trees of an appropriate size for the width of the planting strip that will not conflict with other infrastructure.

Comments

Speaking of creative sidewalk solutions, what’s the story on rubber sidewalks? Your official page on them (http://www.seattle.gov/transportation/rubbersidewalks.htm) hasn’t been updated in over 4 years. They’re a dream to walk on (especially after a few miles of concrete), and I always hope I’ll come upon more of them in my ramblings. Is the pilot still ongoing? If it’s done, what were the results?

SDOT has used recycled pavers made by RubberSidewalks at three locations. Flexibility and ease of repair are some of the benefits of the product when it is installed in areas vulnerable to root heave. However, SDOT’s installation costs were about twice as much as placing sidewalk with standard concrete. Given that SDOT must stretch every dollar, use of alternative sidewalk materials must be carefully evaluated to ensure the City gets a good return on our investment in infrastructure maintenance. Another product SDOT has looked into are a new paver also made by RubberSidewalks, Incorporated. These are made of recycled plastic and rubber and are simpler to install. Kirkland and Olympia are currently testing the product and we are monitoring their results.